Method of and apparatus for transmitting signal control currents



Aug. 28, 1934. L. ESPENSCHIED METHOD OF AND APPARATUS FOR TRANSMITTING SIGNAL CONTROL CURRENTS 2 Sheets-Sheet 1 Filed Feb. 20. 1931 J Y R 0. Td m E 0 Wm Ur I5 A m B L Aug. 28, 1934. L. ESPENSCHIED METHOD OF AND APRKREPUS FOR TRANSMITTING SIGNAL CONTROL CURRENTS Filed Feb. 20, 1931 2 Sheets-Sheet 2 mvzzvroze L. [sparse/fled BY A TI'ORNE Y5 Patented Aug. 28, 1934 METHOD OF AND APPARATUS FOR TRANS- MITTING SIGNAL CONTROL CURRENTS Lloyd Espenschied, Kew Gardens, N. Y.

18 Claims.

This invention relates to the transmission of signal-control current over lines which serve also to transmit a supply of alternating current of a frequency (herein referred to as the original frequency) which is different from the frequency of the signal current. It has for an important object to contrive a method and apparatus whereby a current suitable for the control of a signal, an indicator or automatic control device may be transmitted over a circuit at a frequency close to that of the alternating current supply, and may be completely and efficiently separated out at the signal location with full protection against the effect of higher voltage of the current supply frequency, herein called original frequency.

The signal control channel is to be transmitted, for example, from a point of signal origin (called point of signal control) to a point at which the signal indication or control is utilized (termed point of signal location) In accordance with one method of practicing the invention, the impression of the control frequency on the line at the point of signal control, and likewise the deriving of the control frequency from the line at the point of signal location is accomplished by, in effect, modulating the control frequency with the original or current supply frequency. At the point of signal location this modulating action results in translating the frequency of the control channel to a different frequency (or frequencies), one which, in fact, differs from the original frequency by the value of the control frequency itself. This different frequency (or frequencies) is then propagated over the transmission circuit to the point of signal location. There it is again modulated with the original frequency. This results in its being translated back to the control frequency, in its being separated from the original frequency and becoming available to govern the signal or control device.

In accordance with the particular embodiment of the method which is herein illustrated, there is used at the point of signal'control a static or motionless device for effecting the modulation: At the point of signal location there is disclosed the use of both a static and a dynamic type of modulating device for demodulating out the control frequency. Another important phase of the illustrated embodiment of the invention is that it is the generator of the original frequency itself which constitutes the dynamic modulating ele ment forseparating out the control frequency.

\ Taking for example, an original frequency of cycles per second and a control frequency of 25 cycles per second, the return transmission may Application February 29, 1931, Serial No. 517,354

be regarded as including current having the sum frequency of cycles per second and current having the difference frequency of '75 cycles per second. These frequencies are close enough to the original frequency to be transmitted efficiently through transformers designed to pass the original frequency. Because they are so close to the original frequency, however, there would ordinarily be difficulty in separating them out at the points of signal control and signal location.

In accordance with the present invention, this diificulty is overcome by taking off the control transmission through a frequency translator, such as a machine operating synchronously with the current of original frequency. In accordance with the assumption that the frequency of this machine is 100 cycles, the machine is efiective to derive from the transmission line for signal control purposes a frequency of 100-75:25 cycles, and 100+125=25 cycles. Any variation in the original frequency willbe self-compensating since this frequency cancels out in the overall result in respect to the control channel.

The present application is a continuation in part of my pending application Serial No. 693,787, filed February 19, 1924 for Railway signalling, and, as in said application, the invention is illustrated and described as applied to a locomotive cab signalling system. The Figure 1 and. 2 disclosures hereof have been taken in their entirety from said application. When so applied, the original frequency may be generated on the locomotive and transmitted along the wayside circuit to the point of signal control, e. g., the entrance of the next blockahead at which point the modulation is effected in accordance with the traffic conditions in said block. The current resulting from this modulation is then sent back from the point of signal control to the locomotive at which it is received, segregated from the original frequency, and caused to operate the cab signal or control apparatus.

The invention in a broader aspect is not limited to the taking off of the signal current through the generator of the current of eoriginal frequency,

since the signal current may be taken off at any desired point along the line by means of apparatus operated synchronously with the generator of the current of original frequency.

The invention has a wide range of utility, being applicable not only to train control systems but systems.

Other objects and advantages will hereinafter appear.

' also to power distribution systems and to other In the drawings forming part of this specification,

Figure 1 is a view illustrating one form of embodiment of the invention;

Figure 2 is a view showing a modification of the cab circuits shown in Figure 1; and

Figure 3 is a view showing a modification in which the invention is applied to an electric power transmission.

In the illustrative embodiment of Figure 1, the railway track 1 is divided into sections of which four are shown, namely A, B, C, and D. The railway vehicle 3 is provided with a source of alternating current S, which source is connected through a tuning condenser to a coil 4 spaced in inductive relation with the track rails. The coil thus associated inductively with the rails of the track serves to impress single frequency current from source S on the rails of the track. Two inductor coils, one associated with each track rail, may be employed in accordance with well known practice.

In Figure 1, the vehicle 3 is shown as occupying section B. The insulated joints 2 confine the current impressed on the track to section B.

At the exit end of the block, this current enters a modulator M which, in the specific form of embodiment, is shown asbeing of the magnetic type. It will be understood, however, that'any other .type of modulator, including amplification where required, may be employed. In the illustration, the'modulator is shown as provided with windings 21 and 22, the former of which is connected through leads 25 to the track rails, and the latter. of which is connected through leads 26 to the source of current supply E shown in the drawings as the transmission line 27, supplied with alternating current by a generator F. This line serves also to convey polarizing current to the modu lators from direct current generator G, inductances '71 being provided to minimize the flow of alternating current through the generator G and a transformer '70, including a condenser, being furnished to-exclude the direct current from generator F.

In cases where the superposition of the tw currents on the same line is not justified, separate-power supply lines may, of course, be employed. v

The modulated current from M, i. e. the current of the third" or different frequency, is returned through leads 25 to the track rails and from there enters the coil 4 and source S. At this point the current of different frequency is segregated from the current of original frequency and caused to'efiect the desired signal or control operation. This segregation may be effected by tuned circuits if the percentage difference in the frequencies of the currents is sufilciently great. Where the difference is insumcient, however, the present invention provides a means for so converting the frequencies that they. may be separated by properly tuned circuits.

For purposes of illustration it wmpe assumed in the present example that the frequency of source S is 100 cycles and the frequency of source E is 25 cycles so that the sum and difference frequencies .returned to the vehicle from modulator M are 125 and '75 cycles. The'difference between the outgoing and returning frequencie'sis not great and ordinary tuned circuits cannot well be relied upon to effect v their segregation, particularly where it is necessary to guard against the h'azardof high voltages. In accordance with the present invention, however,'the sum and difierence frequencies are so converted that they may be readily segregated from the original frequency, that is, from the frequency of source S. The apparatus for efiecting this conversion of the frequencies is as follows: x

In the illustrative form of Figure 1, source S comprises an alternator 28 having a field winding, 29 and a direct current exciter 30, the current from the exciter being impressed on the field through leads 31. The current received by coil 4 of the vehicle enters the circuit of the armature of alternator 28 and passes by induction into field winding 29.

The relative motion between the armature and the field, however, effects what is essentially a modulation, or what might be termed a demodulation or detection of the magnetic fields set up in the armature by the received currents. Thus, the alternating armature magnetic field generated by the received currents is modulated at a cycle rate which is the frequency equivalent of the rotational speed of the machine.

As is now well known, the eifect of modulating received currents of one set of frequencies in accordance with another frequency is to set up two 100 new sets of frequencies, one representing the original set of frequencies plus, and the other the original set minus, the frequency of modulation. Thus, for each of the two frequencies which are returned from modulator M, two new sets of frequencieswill be generated in the field winding. In each case the components representing the sum terms are not useful and can be neglected. The components representing the difference terms come out to be 100 minus 75 equals plus 25 cycles and 100 minus equals minus 25 cycles. The phase relations are such that the plus 25 and the minus 25 cycle components are additive in the field winding so that a 25 cycle current is set up. The components of the return 1 5 transmission which are used to convey the signal indication are therefore transferred over to the field windings as a 25 cycle current with the originally generated current of 100 cycles completely eliminated and absolutely unable to get 120 into the receiving channel.

The current thus derived is employed to govern I signal and control apparatus not shown in the drawings, an alternating current relay 33 being employed for effecting this control. Separation 25 of the direct current from the exciter and thealternating current from the field winding is eifected by means of a condenser 34 in series with the'relay and an anti-resonant circuit .35 in series with the exciter armature. The. condenser 34- also tunes the circuit of the relay to obtain the ma um flow of current. A suitable amplifier, not' shown in the drawings, may be provided in the circuit between the field winding 29 and relay 33 in order to increase the power available for 3 the operation of the relay.

It will be observed that the modulator M is controlled by track circuit apparatus illustrated by relay T bridged across the track rails and supplied with current by the track circuit energized from the transmission line E through the transformer 70, the secondary side of which is connected to the track rails by the leads 25. Choke coils '71 and condensers 72 are provided in this connection to prevent the current of original fre' quency entering and leaving modulator M from enteringtransmission line E, and to preventthe low frequency current of transmission line E from entering the modulator M, without being subjectto the control of the tramc conditions return transmission.

ahead. These frequency-discriminating elements may, where necessary, be enlarged into more complete filters. It will thus be observed that the low frequency source of signal current is employed for two purposes, first, to control the track relays T, and second, to modulate the original current transmitted from the vehicle in order to provide the desired third frequency or frequencies of The low frequency 25-cycle signal current which passes through transformer to the rails,

for the purpose of operating relay T of the ordi-v nary block signal track circuit, does not pass through the train-carried receiving circuit and operate-continuously the relay 33 because the train circuits are designed to exclude this lower frequency current and select the higher frequency currents of 100 :25 cycles. Thus, the circuit of the train inductor 4 is tuned by condenser 50 to present a high impedance to the 25-cycle current. Such small 25-cycle current as may find its way into the rotor winding 28 of alternator S is transferred to the stator winding 29 at quite a different frequency by virtue of the frequencyconverting action of the machine. Actually, it appears in the field winding as 25+60=85 cycles and as 2560=35 cycles. Such currents are then further discriminated against in the circuit which connects the stator winding 29 with the relay 33 because that circuit is tuned to the desired 25-cycle demodulated current by means of condenser 34. Thus, the train receiving circuit will be seen to set up a two-fold selection against an interfering action on the part of the 25-cycle block signal current, first, the frequency selection of the tuned traininductor 4, and, second, the frequency converting action of alternator" S, plus the frequency selection of its tuned field circuit.

Figure 2 illustrates a modification of the apparatus carried by the vehicle. Current of the desired frequency, in the present instance 100 .cycles, is generated by the vacuum tube oscillator 80 consisting of an electrontube 81 provided with an input circuit consisting of a portion of the turns of the track coil 4 connected between the filament and the grid, and an output circuit comprising the remaining turns of the track coil 4 and B battery 82 connected between the filament and the plate. A condenser 83 is connected in shunt to coil 4 and bears such relation to the inductance of coil 4 that the oscillations are of the desired freuency, namely, 100 cycles per second. The grid of the oscillator is made sufficiently negative by means of a. grid condenser 84 to cause the tube to function also as a detector. The current thus generated is transmitted into the wayside circuit and travels toward the distant end of the block as in the case of Figure 1. The returning frequencies of 125 and cycles enter the coil 4 and pass through the circuits of the oscillator, and by virtue of modulation therein with the 100 cycle current being generated are converted into a 25 cycle current. This 25 cycle current is separated from the direct current component of the plate current by a transformer and condenser, as shown, and is caused to energize an alternating current relay, 84a. Further filtering elements may, of course, be added in the output circuit of the transformer. The relay 84a is connected to a suitable signal and control apparatus not shown in the drawings. An amplifier of any suitable type, indicated in the drawings by reference character 85, may be provided for reinforcing the received current.

It will be noted that in both the embodiments illustrated in Figures 1 and 2, the generator of the outgoing or original" frequency current acts simultaneously as a modulator or detector of the returning current to step down the frequency and to thus facilitate the segregation of the one current from the other. Particularly is this true of the embodiment of Figure 1, since the mechanical rotation of the alternator automatically prevents any current of the original frequency from flowing through to the receiving circuit. In both embodiments, any fluctuations in the frequency of the outgoing current are automatically compensated for in receiving, since the same fluctuations are simultaneously taking place in the demodulation of the returning current, so that the frequency of the relay operating current remains unaffected by such fluctuations;

While the invention has been illustrated herein as applied to a railway signalling system, it is apparent that the invention has a wide range of utility and is also applicable to power distribution systems and to other systems. An important advantage of the method herein disclosed as applied to power distribution systems is that it enables the control impulses to be passed over the power system at frequencies close to the power frequency itself, which means that these control frequencies can be passed over the power system, can be efiiciently transmitted through the power transformers, and can be superimposed A machine operated synchronously with such generator.

The application of the invention to an electric power transmission system is illustrated in Fig. 3. In order to simplify the explanation, a s'.nglephase system is illustrated. The manner of applying the invention to a multi-phase system' will be apparent to those skilled in the art. The portion 101 represents the generating end of the system, 102 the transmission line, and 103 the lower tension distribution end of the system. .1 More spec'fically, the power system comprises the alternator 104, the step-up transformer 105, the pair of conductors 106, constituting the high 'tension transmission line, the step-down transformer 107, and the lower voltage distribution line 108. The alternator is provided with the usual field winding 109 and an exciter 110.

The signal control circutis introduced into the alternator field circuit by means of a transformer 111, one winding of which is connected in series therewith. The other winding connects through a circuit 112, 112' and 113, 113' to a source of alternating signaling current 114. This source is illustrated as an alternator, driven synchronously with the power generator 104. The circuit includes a signal control switch 115, controlled by the relay winding 116.

At the other end of the power transmission system there is provided for taking air the signal control channel a circuit which includes conductors 117, 117', transformer 118 and synchronous motor 119. The field winding 120 of this motor connects with winding 121 of an induction type relay 122. The other winding 123 of the relay is excited by alternating current supplied from a small generator 124, driven synchronously with motor 119, as by being mounted on the same shaft.

The operation of this combined power and sig- 5 nal control system will be most readily understood by taking a concrete example. Assume the power supply frequency generated by alternator 104 to be 60 cycles per second and the signal control current frequency generated by the smaller alternator 114 to be of lower frequency, say, 10 cycles per second. With control switch 115 closed, the 10-cyc1e current passes through transformer 111 into the field circuit of the power alternator 104. The 10-cycle current passes through thealternator 104 as a transformer, but as a result of the rotation of the alternator is modulated at a (SO-cycle rate and is transformed to 60:10, or 50 cycles and cycles. The signal control current, therefore, is transmitted over the power system as current of two frequencies, 50 and 70 cycles. These currents are so near in frequency to the power frequency of 60 cycles as to be transmitted efficiently over the line and through all power transformers, such as 105 and lu't.

At the distribution end of the system the, signal control currents are transmitted into and are absorbed by the many loads fed by the power system. They are present throughout ,the distribution system, available, however, to be picked up and made to operate signal or control devices as desired at substations or at load points. The signal terminal shown at the right-hand side of Fig. 3 is intended to illustrate the circuit for one such control device. The operation is as follows: Passing through the step-down transformer 118 are both the power supply current of 60 cycles and the weaker signal control currents of 50 and 70 cycles. The motor 119 is driven by the power current, and rotates synchronously therewith. It ,is operated without load and serves only as.a frequency transformer for the signal current. Each of the two signal current components is modulated by the rotational frequency of this motor and appears in the field winding at a transformed frequency. Thus, the 50-cycle signal current component becomes 50-60 or 10 cycles and 50+60 or 110 cycles; and the 70-cycle component becomes IO-60 or 10 cycles and 70+60 or 130 cycles. Currents at frequencies 10, 10, 110 and 130 cycles appearin the field 120 of the synchronous motor. The two 10-cycle currents come out in phase and are used in operating the receiving relay 122. The other two frequencies are ineffective in operating the relay. They may be suppressed by means of a filter inserted in the circuit between the field winding 120 and the relay winding 121. The other winding 123 is excited by 10-cycle current supplied by alternator 124, which is designed to give 10-cycle current of proper phase when driven synchronously with motor 119.

It will be observed that the 10-cycle received current is the same frequency as was originally applied to the power system at the sending end. Also, it will be noted that at both the sending end and the receiving end the 10-cycle signal circuit is completely free of 60-cycle power current. This complete separation is obtained by the use of the synchronously rotating machines which completely suppress the power frequency from the signal terminal circuits.

The'signal control channel of Fig. 3 is capable of transmitting three indications; one corresponding to current off (with the contacts of control switch 115 open and the receiving relay 122 released, as shown) a second with the movable arms of switch 115 thrown to the left and the control arm of receiving relay 122 likewise thrown to the left; and a third with the contacts of switch 115 and of relay 122 thrown to the right. The throw-over between the second and the third indication will be noted to be accomplished by a reversal of the phase of the lowfrequency control current. The receiving relay is capable of responding to this reversal by virtue of the interaction between the currents of the same frequency in the receiving relay windings 121 and 123.

It is apparent that other types of receiving relays may be employed. For example, at the terminals 125 there may be connected a rectifier operating a D. C. relay. It will also be realized that the signal control channel may be transmitted over the power system in the reverse direction from that illustrated, by interchanging the transmitting and receiving terminals of the .signal control channel. Although the rotary frequency translators as exemplified by the ma-, chines 104 and 119 possess certain advantages, the application of the invention to power distribution systems is not limited to this type of device. There may be employed static frequency translators such as magnetic or vacuum tube devices for either modulating the signal control channel upon or demodulating it from the power supply current as has been indicated in connection with Figs. 1 and 2. The features characterizing the invention are set forth in the claims following.

Although I have herein shown and described only certain specific forms of embodiment of the invention, it will be understood that the same is not limited thereto, but that various changes and modifications may be made therein within the scope of the accompanying claims, without departing from the spirit and scope of the invention.

What I claim is:

1. In a signal control system, a transmission circuit, carrying alternating current, means for superimposing upon said current a second variation differing in frequency from the frequency of said current, a dynamo-electric machine connected to said transmission circuit and rotating synchronously with respect to said first named alternating current, together with connections to the field winding thereof for conveying current of said second variation to a receiving device.

2. A generator of alternating current functioning to deliver current of one frequency, a line circuit therefor, means connected to said circuit for impressing upon said current a second periodic variation of frequency different from the first frequency and for controlling said different frequency in accordance with indications, together with connections taken from said generator for delivering current at said diiferent frequency. I

3. In a system comprising a power supply circuit and a connected signal or control circuit, the arrangement for excluding the power supply current from the signal circuit which comprises an inductive translating device running synchronously with the frequency of the power supply current and means for connecting the translating device between the control circuit and the power supply circuit.

4. The combination with an electric circuit of means for energizing it with alternating-current electric power, of means for transmitting thereover a superimposed channel differing in 1,971,483 frequency from the frequency of the power supply current, together with frequency changing means connected directly with said electric circuit and operated synchronously with the power supply current to lead off the superimposed channel to the exclusion of the power supply current.

5. A system comprising an alternating current power supply circuit, a superimposed signal or control channel operating at a frequency different from that of the power supply circuit, means for selecting the signal channel to the exclusion of the power supply current including frequency changes operating synchronously with the frequency of the power supply current.

6. A system comprising an alternating current power supply circuit, a superimposed signal or control channel operating at a frequency different from that of the power supply circuit, and frequency changing means operating synchronously with the power supply frequency for connecting the signal channel with a terminal signal circuit to the exclusion of the power supply current.

'7. A system comprising an alternating current power supply circuit, a superimposed signal or control channel operating at a frequency different from that of the power supply circuit, and means comprising the windings of a synchronous machine for translating between the superimposed signal channel and the signal terminal circuit from which the power current is excluded.

8. The combination with an electric circuit of an A. C. generator for energizing the circuit, means for impressing on said circuit control current differing in frequency from the frequency of the generator, and means for taking off the control current from the circuit through said generator.

9. 'Ihe'cornbination with an A. C. electric circuit transmitting current of a first frequency, and means for impressing on said circuit control current of a second frequency, of means for detecting out the resultant current and taking off from the circuit the current of the second frequency comprising a frequency translating device operating synchronously with the frequency of the current of said first frequency.

10. The system for superimposing a control channel upon an alternating current power supply circuit comprising means at both the transmitting and receiving terminals of the control channel for adding-to or subtracting from the frequency of the control channel the frequency of the power supply circuit, said means at one of said terminals constituting the two sets of windings of a machine operating synchronously with the power supply frequency.

11. The method of superimposing a signal indicating or a control channel upon a powersupply circuit which consists in translating the frequency of the indicating or control channel to a frequency which differs from the frequency of the power supply current by the amount of the first named frequency, transmitting said channel over the power-supply circuit and finally subjecting said channel to the frequencytranslating action of a transformer the coupling between the two sets of windings of which is varied synchronously with the power supply frequency, and thereby deriving current of the frequency of the indicating or control channel to the exclusion of the power supply current.

12. In combination, an alternating current power-supply circuit, a control or indicating channel superimposed thereon, means at the points'of superposition for adding to or subtracting from the frequency of the powersupply current the frequency of the control channel whereby the control channel is transmitted over the power circuit at an altered frequency, said means at one of said superposition points comprising a synchronously operating dynamo-electric machine functioning as a frequency changing transformer.

13. In a system for transmitting control impulses over an alternating-current supply circuit which includes a dynamo-electric machine operating synchronously with the frequency of the supply current and provided with an exciting winding, the method which consists in impressing a current of other frequency upon the circuit, subjecting said current of other frequency to the frequency-translating action of said synchronous machine, and finally taking from the exciting winding of said machine a current representing in frequency the difference between said other frequency and the frequency of the supply current itself.

14. In a power supply circuit of a definite frequency, a system for transmitting another frequency over said circuit including a synchronous machine of the circuit'frequency, an exciting winding for said synchronous machine, and means for passing a second frequency through the exciter circuit of said machine.

15. In a power supply circuit of a definite frequency including a synchronous generator, a system for superimposing another frequency on said circuit comprising means for connecting a circuit of second frequency to the exciter circuit of such synchronous generator.

16. In an electrical circuit carrying currents of definite frequency, means to connect thereto a circuit carrying currents of a different frequency, said means comprising coupling elements moving with respect to each other at a speed synchronous with said definite frequency and means .for applying a second frequency to one of said coupling elements.

17. In combination with a systen carrying alternating currents of definite frequency, means for connecting thereto a circuit carrying currents of a different frequency, said means comprising a coupling device associated with said system and having primary and secondary members, one of said members being constantly driven in respect to the other one of said members in synchronism with said definite frequency, thus preventing electric coupling for this frequency and means to supply current of frequency different than said definite frequency to said coupling device.

18. Means for translating between a circuit supplying energizing current to a distance point and a circuit for operating a signal or control device, which comprises a machine connected with its armature winding to an alternating current supply circuit and operating synchronously with the current in said circuit, and with its exciting windlng connected to a signal or control device.

LLOYD ESPENSCHIED. 

